The vulnerability allows an attacker to trigger a denial of service by sending an invalid U-format frame to a Hitachi Energy RTU500 series CMU firmware device when IEC 60870‑5‑104 bi‑directional functionality is enabled. The invalid frame is processed during reception, potentially causing a hang or reset of the communication stack. The flaw, identified as CWE‑184, is rated with a CVSS score of 8.7, marking it high severity. While enabling secure communication per IEC 62351‑3 does not patch the flaw, it reduces the likelihood that malicious frames reach the device.

This defect affects the Hitachi Energy RTU500 series CMU firmware used in RTU520, RTU530, RTU540, and RTU560 devices. All models running firmware version 13.8.1 are known to be vulnerable, as are devices operating any prior firmware that includes the same vulnerable code path.

The likelihood of exploitation is reflected in an EPSS score of less than 1 %, suggesting that known exploitations are rare or limited. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog, but the high CVSS still warrants remediation. An attacker would need network access to the IEC 60870‑5‑104 channel and the ability to transmit malformed frames; enabling secure communication per IEC 62351‑3 mitigates the risk but does not eliminate the vulnerability.